Add Netlify configuration.

- The netlify.toml file explains how to build this site for production
  and deploy previews.
- The Makefile has some commands to make building the site slightly more
  user friendly, try typing `make help`.
- The Gemfile includes all the dependencies exported from GitHub Pages.
  This site might not need all of the but I don't have the knowledge to
  exclude the unused ones.

Signed-off-by: David Calavera <david.calavera@gmail.com>

Makefile

@@ -0,0 +1,15 @@
+.PONY: all build build-preview help serve
+
+help: ## Show this help.
+	@awk 'BEGIN {FS = ":.*?## "} /^[a-zA-Z_-]+:.*?## / {sub("\\\\n",sprintf("\n%22c"," "), $$2);printf "\033[36m%-20s\033[0m %s\n", $$1, $$2}' $(MAKEFILE_LIST)
+
+all: build ## Build site with production settings and put deliverables in _site.
+
+build: ## Build site with production settings and put deliverables in _site.
+	jekyll build
+
+build-preview: ## Build site with drafts and future posts enabled.
+	jekyll build --drafts --future
+
+serve: ## Boot the development server.
+	jekyll serve